We propose to perform a series of parametric experiments on healthy student subjects to study two event-related potential (ERP) components which appear to reflect cognitive processing, but which can be elicited automatically. Such components should be useful in cognitive evaluation of patients unable to cooperate with usual cognitive testing procedures. The components, both of which can be elicited even when subjects are distracted, are the P300 elicited by brief, high intensity noise bursts and a negative-positive complex (Ne-Pe) elicited by a changes of pace in auditory stimulus presentation (pace change components). Among the specific aspects of the automatically elicited P300 to be investigated are the effects of stimulus rise time, duration, and temporal uncertainty on it. Paradigms in which interstimulus intervals allow simultaneous measurement of skin conductance and heart rate responses will be used to place this ERP component in the context of a more general psychophysiology of reactions to simple stimuli. Additional experiments will investigate the extent to which automatic elicitation of P300 draws cognitive resources from concurrent controlled processes. Among the specific aspects of the pace change complex to be investigated are the effects of uncertainty as to time of occurrence of timing deviations, effects of the degree of deviation, and the extent to which a pace change components habituate.